RX J1856.5-3754 (also called RX J185635-3754, RX J185635-375, and various other designations) is a nearby neutron star. It is believed to have been created by a supernova explosion of its companion star about one million years ago, and is moving 108 km/s across the sky. It was discovered in 1992, and observations in 1996 appeared to confirm that it was a neutron star, the closest neutron star to Earth yet discovered. The distance was thought to be about 150–200 light years away. However, further observations using the Chandra X-Ray Observatory in 2002 appear to show that its distance is greater (about 450 light years). It was once proposed that RX J1856.5-3754 was too small to be a neutron star, and may therefore in fact be a quark star. However, this theory is not currently considered to have much supporting evidence.
- ESO Press Release 19/00: The Mystery of the Lonely Neutron Star
- Closest Known Neutron Star Races Across Sky (space.com)
- Is RX J185635-375 a Quark Star?
- APOD: 2002 April 14 - RX J185635-375: Candidate Quark Star
- Bare Quark Stars or Naked Neutron Stars? The Case of RX J1856.5-3754
- RX J185635-3754 - an Isolated Neutron Star